Co-modulation Of Graphene By Hetero-doping & Vacancy Defects And The Effect On Gas Sensing Applications:First-principles Study

This work based on the calculation method of first-principles density functional,using Materials Studio software,studied the effect of co-modification by nitrogen atoms and vacancy defects in single-layer graphene on its gas sensitivity and selectivity.Modulation by hetero-doping or vacancy defects has been proved effective on gas-sensing response enhancement of intrinsic graphene.To explore the synergistic effect of hetero-doping and vacancy defects,in this work,the adsorption of NO₂molecule on the defective graphene co-modulated with N-doping and c-vacancy was studied using first-principles calculations.The doping&vacancy models of defective graphene were constructed by creating single/double c-vacancies with partial or total marginal c atoms around the defect substituted by N atoms.Based on the super cell models of intrinsic graphene,vacancy graphene and N-doping graphene,we calculated the band structure of the three basic models and considering three different adsorption configurations of NO₂.The structure of the nitrogen end adsorption was determined.In the subsequent study of NO₂adsorption on the co-modified graphene models,we classify models according to the vacancy concentration,and the calculations about adsorption energy,DOS and atomic Mulliken population reveal that the sub-fully doped configurations,i.e the N₂V₁in the single vacancy system and the N₃V₂model in the double vacancies system,achieved significant enhancement for NO₂adsorption and interaction with the defective surface in corresponding vacancy systems.Further analysis on geometry and charge density difference demonstrates that the sub-full doping of N atoms causes strong asymmetry in charge distribution around the vacancy,which is further correlative to the improved adsorption characteristic of the co-modulated graphene from the perspective of a local built-in electric field.Then we built different gas molecules（NH₃,CH₄,HCHO,CO）adsorption models on the surface of the sub-full doped graphene to study the selectivity of multiple gas.The transferred electrons after adsorption could quantitatively response the sensitivity of difference gas molecule adsorbed on the sub-full doped graphene,and also could know which gas behaved most selectivity.In summary,the present work provides theoretical understanding for the effect of nitrogen-doping and vacancy co-modification on NO₂sensing mechanism of graphene-based sensor and pointed out that the sub-full doped graphene has the best result.And it has good resistance to other gases（NH₃,CH₄,HCHO,CO）when detecting NO₂ gas.